An examination of the epiphytic nature of Gambierdiscus toxicus, a dinoflagellate involved in ciguatera fish poisoning

Twenty-four specimen of macroalgae were collected in nearshore waters of the island of Hawaii, identified, and maintained to examine how the epiphytic relationship between Gambierdiscus toxicus (isolate BIG12) varied among the macroalgal species. Gambierdiscus cells were introduced to Petri dishes containing 100 g samples of each macroalgal host, which were examined at two, 16, 24, and every 24–72 h thereafter, over a 29-day period. Gambierdiscus proliferated in the presence of some host species (e.g., Galaxaura marginata and Jania sp.), but grew little in the presence of other species (e.g., Portieria hornemannii). Gambierdiscus exhibited high survival rates (>99%) in the presence of Chaetomorpha sp., but died before the end of the experiment (after 21 days) with other host species (e.g., Dictyota and Microdictyon spp.). Gambierdiscus avoided contact with P. hornemannii, but averaged up to 30% attachment with other host species. The numbers of Gambierdiscus cells belonging to one of three classes (alive and attached; alive and unattached; and dead) were determined for each time point. The 24 algal hosts were grouped according to their commonalities relative to these three classes using a Bray-Curtis similarity index, similarity profile (SIMPROF) permutation tests, and Multi-Dimensional Scaling (MDS) analysis (PRIMER 6). The resultant six groupings were used to construct different Gambierdiscus growth profiles for the different algal hosts. Group A is characterized by a preponderance of unattached cells and high mortality rates. Groups B, C, E, and F also displayed high proportions of unattached cells, but mortality either occurred later (Groups B and C) or rates were lower (Groups E and F). Group D had the highest proportion of attached cells. Group E contained three out of the four chlorophyte species, while Group F contained the majority of the rhodophytes. Over 50% of the species in Group F are considered to be palatable, whereas Groups A, B, and C are composed of species that exhibit chemical defenses against herbivory. The results of this study coupled with previous findings indicate that Gambierdiscus is not an obligate epiphyte; it can be free-swimming and found in the plankton. The conditions that lead to changes between epiphytic and planktonic stages need to be better studied in order to determine how they affect Gambierdiscus growth and physiology, connectivity and dispersion mechanisms, and toxin movement up into the foodweb.     

Multi-species okadaic acid contamination and human poisoning during a massive bloom of Dinophysis acuminata complex in southern Brazil

On June 2016, a major bloom of Dinophysis acuminata complex was noticed over the coast of Paraná State (PR), southern Brazil, an area unprotected by any official monitoring program. Here we report the results of an extensive sampling effort that ultimately led PR authorities to issue the first State shellfish-harvesting ban due to multi-species okadaic acid (OA) contamination. During its peak, the bloom covered an area of 201 km² (∼2.0–3.5 × 54.0 km), attaining unprecedentedly high cell densities along the shallow (<15 m) continental shelf (mean 2.2 × 10⁵, maximum 2.1 × 10⁶ cells L⁻¹) and adjacent sandy beaches (mean 2.8 × 10⁵, maximum 5.2 × 10⁶ cells L⁻¹). Only OA was detected in suspension (max. 188 ng L⁻¹). Toxin levels measured in bivalves were several times greater than the regulatory limit of 160 ng g⁻¹, reaching up to 3600 ng g⁻¹ in Crassostrea gasar, by far the highest OA concentrations ever reported in oysters worldwide, 7700 ng g⁻¹ in brown mussels, Perna perna, and lower levels in clams, Anomalocardia brasiliana, and mangrove mussels, Mytella spp. Nine cases of human intoxication were officially reported and five people were hospitalized with typical symptoms of Diarrhetic Shellfish Poisoning linked to the consumption of contaminated bivalves. All bivalves quickly converted most of the OA into its esterified form, DTX-3, and eliminated the toxins only a few weeks following the bloom, with C. gasar being the slowest-detoxifying species. Lower OA levels were accumulated in zooplankton, gastropods and several novel toxin vectors, including benthic organisms such as sand dollars Mellita quinquiesperforata and the ghost-shrimp Callichirus major, which may act as a good indicator of the presence of toxins in sandy beaches, and pelagic fish species that can serve as potential alternative sources of OA to humans (Chaetodipterus faber and Mugil liza). Monitoring toxin contamination in seafood other than bivalves is thus recommended to ensure comprehensive human health protection during massive Dinophysis blooms. Additionally, since OA was also present at low concentrations in the liver of Guiana dolphins Sotalia guianensis and penguins Spheniscus magellanicus, exposure to biotoxins should be considered in conservation actions involving threatened and near-threatened marine organisms in this region.     

Trends in Dinophysis abundance and diarrhetic shellfish toxin levels in California mussels (Mytilus californianus) from Monterey Bay,California

Diarrhetic shellfish toxins (DSTs) are produced by the marine dinoflagellate, Dinophysis, as well as select species of benthic Prorocentrum. The DSTs can bioaccumulate in shellfish and cause gastrointestinal illness when humans consume high levels of this toxin. Although not routinely monitored throughout the U.S., recent studies in Washington, Texas, and New York suggest DSTs may be widespread throughout U.S. coastal waters. This study describes a four-year time series (2013–2016) of Dinophysis concentration and DST level in California mussels (Mytilus californianus) from Santa Cruz Municipal Wharf (SCMW) in Monterey Bay, California. Results show a maximum Dinophysis concentration of 9404 cells/L during this study and suggest Dinophysis persists as a member of the background phytoplankton community throughout the year. In California mussels, DSTs were found at persistent low levels throughout the course of this study, and exceeded the FDA guidance level of 160 ng/g 19 out of 192 weeks sampled. Concentrations of Dinophysis alone are a positive but weak predictor of DST level in California mussels, and basic environmental variables (temperature, salinity, and nutrients) do not sufficiently explain variation in Dinophysis concentration at SCMW. This study demonstrates that Dinophysis in Monterey Bay are producing DSTs that accumulate in local shellfish throughout the year, occasionally reaching levels of concern.     

Effective aerial monitoring of cyanobacterial harmful algal blooms is dependent on understanding cellular migration

Cyanobacterial harmful algal blooms (CHABs) degrade water quality and may produce toxins. The distribution of CHABs can change rapidly due to variations in population dynamics and environmental conditions. Biological and ecological aspects of CHABs were studied in order to better understand CHABs dynamics. Field experiments were conducted near Hartington, Ontario, Canada in ponds dominated by Microcystis aeruginosa and CHABs floating experiments were conducted at Lake Taihu during the summers of 2015 and 2016. Single colonies composed of hundreds to thousands of cells with an average median of 0.2–0.5 mm in diameter were the basic form assumed by the Microcystis, and this remained the same throughout the growing season. Thorough mixing of the water column followed by calm conditions resulted in over 90% of the cyanobacteria floating after 1 h. Multiple colonies floated on the water surface in four types of assemblages: aggregates, ribbons, patches, and mats. It is the mats that are conventionally considered the blooming stage of cyanobacteria.Presence of CHABs on open water surfaces also depends on environmental influences such as direct and indirect wind effects. For example, field tests revealed that the surface coverage of CHABs can be reduced to half within an hour at wind speeds of 0.5 m/s.Because our findings indicated that blooming involves surface display of cyanobacteria essentially presenting as a two-dimensional plane under defined conditions, the use of surface imagery to quantify CHABs was justified. This is particularly important in light of the fact that traditional detection methods do not provide accurate distribution information. Nor do they portray CHABs events in a real-time manner due to limitations in on-demand surveillance and delays between sample time and analyzed results. Therefore, a new CHAB detection method using small unmanned aerial systems with consumer-grade cameras was developed at a maximum detection altitude of 80 m. When cyanobacteria were floating on the surface, CHABs detection through RGB band cameras and spectral enhancement techniques was efficient and accurate. Small unmanned aerial systems were capable of providing coverage up to 1 km² per mission and the short intervals between sampling and results (approx. 2 h) allowed for the rapid analysis of data and for implementing follow-up monitoring or treatments. This method is very cost-effective at an estimate of as low as $100 CAD per mission with an average cyanobacterial detection accuracy of 86%. Thus, it is a good candidate method to fill the urgent need for CHABs detection, providing cost effective, rapid, and accurate information to improve risk management at a local level as well as to help quickly allocate resources for purposes of mitigation.     

Recent domoic acid closures of shellfish harvest areas in Washington State inland waterways

Several species of the toxigenic diatom Pseudo-nitzschia, together with low concentrations of domoic acid (DA) in shellfish have been observed in Puget Sound, Washington State, since 1991. However, for the first time in September 2003, high-density blooms of Pseudo-nitzschia forced the closure of recreational, commercial, and tribal subsistence shellfish harvesting in Puget Sound. Here we report on the environmental conditions associated with shellfish closures in two inland waterways of Washington State during the Fall 2005. In Sequim Bay, shellfish harvest losses occurred on September 12 following the measurement of elevated macronutrient levels on September 2, and a bloom of P. pseudodelicatissima (up to 13 million cells/L) on September 9. Ambient NH₄ concentrations >12 μM (measured on September 2) were likely due to anthropogenic sources, ostensibly from sewage inputs to Sequim Bay. The closure of a Penn Cove commercial shellfish farm on October 16 was caused by a bloom of P. australis that followed a period of sustained precipitation, elevated Skagit River flow, and persistent southeasterly winds. The relative importance of a number of environmental factors, including temperature, stratification caused by rivers, and nutrient inputs, whether natural or anthropogenic, must be carefully studied in order to better understand the recent appearance of massive blooms of toxigenic Pseudo-nitzschia in the inland waterways of Washington State.     

A review of the molecular evidence for ballast water introduction of the toxic dinoflagellates Gymnodinium catenatum and the Alexandrium “tamarensis complex” to Australasia

The potential of ballast water to act as a major introduction vector for toxic dinoflagellates and other phytoplankton is beyond doubt; however, evidence that links the suspected introduced species with a source population is less convincing, especially without supporting historical and biochemical data, or consideration of palaeobiogeographical scenarios that may explain current species distributions. This paper presents new molecular data based on LSU-rDNA and rDNA-ITS sequences that demonstrate an unequivocal and recent link between Temperate Asian and Australasian populations of the toxic dinoflagellates Gymnodinium catenatum and toxic strains of the Alexandrium “tamarensis complex”. We integrate our data with supporting evidence from historical distribution records, sediment dating studies, toxin profiles, mating studies and previous molecular studies. We contrast the observed patterns of genetic and biochemical variation with those expected from various palaeobiogeographical scenarios explaining the evolution and natural dispersal of both species. While definitive proof is impossible, the total evidence indicates that these toxic dinoflagellates were introduced to Australasia during the past 100 years, most probably via ballast water from bulk-cargo shipping from Japan and/or south-east Asia.     

Phytoplankton and bacterial assemblages in ballast water of U.S. military ships as a function of port of origin, voyage time, and ocean exchange practices

We characterized the physical/chemical conditions and the algal and bacterial assemblages in ballast water from 62 ballast tanks aboard 28 ships operated by the U.S. Military Sealift Command and the Maritime Administration, sampled at 9 ports on the U.S. West Coast and 4 ports on the U.S. East Coast. The ballast tank waters had been held for 2–176 days, and 90% of the tanks had undergone ballast exchange with open ocean waters. Phytoplankton abundance was highly variable (grand mean for all tanks, 3.21 × 10⁴ viable cells m⁻³; median, 7.9 × 10³ cells m⁻³) and was unrelated to physical/chemical parameters, except for a positive relationship between centric diatom abundance and nitrate concentration. A total of 100 phytoplankton species were identified from the ballast tanks, including 23 potentially harmful taxa (e.g. Chaetoceros concavicornis, Dinophysis acuminata, Gambierdiscus toxicus, Heterosigma akashiwo, Karlodinium veneficum, Prorocentrum minimum, Pseudo-nitzschia multiseries). Assemblages were dominated by chain-forming diatoms and dinoflagellates, and viable organisms comprised about half of the total cells. Species richness was higher in ballast tanks with coastal water, and in tanks containing Atlantic or Pacific Ocean source waters rather than Indian Ocean water. Total and viable phytoplankton numbers decreased with age of water in the tanks. Diversity also generally decreased with water age, and tanks with ballast water age >33 days did not produce culturable phytoplankton. Abundance was significantly higher in tanks with recently added coastal water than in tanks without coastal sources, but highly variable in waters held less than 30 days. Bacterial abundance was significantly lower in ballast tanks with Atlantic than Pacific Ocean source water, but otherwise was surprisingly consistent among ballast tanks (overall mean across all tanks, 3.13 ± 1.27 × 10¹¹ cells m⁻³; median, 2.79 × 10¹¹ cells m⁻³) and was unrelated to vessel type, exchange status, age of water, environmental conditions measured, or phytoplankton abundance. At least one of four pathogenic eubacteria (Listeria monocytogenes, Escherichia coli, Mycobacterium spp., Pseudomonas aeruginosa) was detected in 48% of the ballast tanks, but toxigenic strains of Vibrio cholerae were not detected. For ships with tanks of similar ballasting history, the largest source of variation in phytoplankton and bacteria abundance was among ships; for ships with tanks of differing ballasting histories, and for all ships/tanks considered collectively, the largest source of variation was within ships. Significant differences in phytoplankton abundance, but not bacterial abundance, sometimes occurred between paired tanks with similar ballasting history; hence, for regulatory purposes phytoplankton abundance cannot be estimated from single tanks only. Most tanks (94%) had adequate records to determine the source locations and age of the ballast water and, as mentioned, 90% had had ballast exchange with open-ocean waters. Although additional data are needed from sediments that can accumulate at the bottom of ballast tanks, the data from this water-column study indicate that in general, U.S. Department of Defense (DoD) ships are well managed to minimize the risk for introduction of harmful microbiota. Nevertheless, abundances of viable phytoplankton with maximum dimension >50 μm exceeded proposed International Maritime Organization standards in 47% of the ballast tanks sampled. The data suggest that further treatment technologies and/or alternative management strategies will be necessary to enable DoD vessels to comply with proposed standards.     

Blooms of Pseudo-nitzschia and domoic acid in the San Pedro Channel and Los Angeles harbor areas of the Southern California Bight, 2003–2004

Abundances of Pseudo-nitzschia spp. and concentrations of particulate domoic acid (DA) were determined in the Southern California Bight (SCB) along the coasts of Los Angeles and Orange Counties during spring and summer of 2003 and 2004. At least 1500 km² were affected by a toxic event in May/June of 2003 when some of the highest particulate DA concentrations reported for US coastal waters were measured inside the Los Angeles harbor (12.7 μg DA L⁻¹). Particulate DA levels were an order of magnitude lower in spring of 2004 (February and March), but DA concentrations per cell at several sampling stations during 2004 exceeded previously reported maxima for natural populations of Pseudo-nitzschia (mean = 24 pg DA cell⁻¹, range = 0–117 pg DA cell⁻¹). Pseudo-nitzschia australis dominated the Pseudo-nitzschia assemblage in spring 2004. Overall, DA-poisoning was implicated in >1400 mammal stranding incidents within the SCB during 2003 and 2004. Ancillary physical and chemical data obtained during our regional surveys in 2004 revealed that Pseudo-nitzschia abundances, particulate DA and cellular DA concentrations were inversely correlated with concentrations of silicic acid, nitrogen and phosphate, and to specific nutrient ratios. Particulate DA was detected in sediment traps deployed at 550 and 800 m depth during spring of 2004 (0.29–7.6 μg DA (g sediment dry weight)⁻¹). The highest DA concentration in the traps was measured within 1 week of dramatic decreases in the abundances of Pseudo-nitzschia in surface waters. To our knowledge these are the deepest sediment trap collections from which DA has been detected. Sinking of the spring Pseudo-nitzschia bloom may constitute a potentially important link between DA production in surface waters and benthic communities in the coastal ocean near Los Angeles. Our study indicates that toxic blooms of Pseudo-nitzschia are a recurring phenomenon along one of the most densely populated coastal stretches of the SCB and that the severity and magnitude of these events can be comparable to or greater than these events in other geographical regions affected by domoic acid.     

Physiological responses of Aureoumbra lagunensis and Synechococcus sp. to nitrogen addition in a mesocosm experiment

Aureoumbra lagunensis is the causative organism of the Texas brown tide and is notable because it dominated the Laguna Madre ecosystem from 1990 to 1997. This species is unusual because it has the highest known critical nitrogen to phosphorus ratio (N:P) for any microalgae ranging from 115 to 260, far higher than the 16N:1P Redfield ratio. Because of its high N:P ratio, Aureoumbra should be expected to respond to N additions that would not stimulate the growth of competitors having the Redfield ratio. To evaluate this prediction, a mesocosm experiment was performed in the Laguna Madre, a South Texas coastal lagoon, in which a mixed Aureoumbra–Synechococcus (a cyanobacterium) community was enclosed in 12 mesocosms and subjected to nitrogen addition (6 controls, 6 added ammonium) for 16 days. After day 4, added nitrogen did not significantly increase Aureoumbra specific growth rate but the alga retained dominance throughout the experiment (64–75% of total cell biovolume). In control mesocosms, Aureoumbra became less abundant during the first 4 days of the experiment but rebounded by the end of the experiment and was dominant over Synechococcus. Despite the lack of a strong positive growth response, Aureoumbra did respond physiologically to N addition. By the end of the experiment, the average N:P ratio of the Aureoumbra-dominated community was 86 in the N+ treatment and 41 in the control, indicating that the alga became less N-limited in the N+ treatment. The average C:N ratio was 6.6 in the N+ treatment (8.6 in the control) and suggests that the alga was not N-limited, however, C:N ratio may not be a good indicator of nitrogen limitation since this alga can produce significant quantities of carbon-containing extracellular polysaccharides, depending on growth conditions. Both Aureoumbra cellular chlorophyll fluorescence and cell size increased in response to added N, indicating a reduction in N limitation. It appeared that the N additions were not large and/or frequent enough to stimulate Aureoumbra growth. The main competitor, the unicellular cyanobacterium Synechococcus, responded positively to the nitrogen addition by increased specific growth rate. Unlike Aureoumbra, no significant effect on Synechococcus cellular pigment fluorescence or cell size was noted. Literature data suggest that Synechococcus, like Aureoumbra, may have a critical N:P ratio much higher than 16:1, which could explain its response.     

广东沿海几种赤潮生物的分类学研究

对１９９７年秋￣１９９８年春广东沿海多次赤潮发生期间的几种优势赤潮藻类进行了形态学和分类学研究。１种为我国首次报道引发赤潮的定革命金藻类（Ｐｒｙｍｎｅｓｉｏｐｈｙｔｅｓ）－球状棕囊藻（Ｐｈａｅｏｃｙｓｔｉｓ ｃｆ．ｇｌｉｏｂｏｓａ）。另有甲藻类７种,其中裸甲藻目（Ｇｙｍｎｏｄｉｎｉａｌｅｓ）３种：米氏裸甲藻（Ｇｙｍｎｏｄｉｎｉｕｍ ｃｆ．ｍｉｋｉｍｏｔｏｉ）、环节环沟藻（Ｇｙｒｏｄｉｎｉｕｍ ｉｎ